Bright copper plating from cyanide baths



Patented Sept. 2, 1952 faeoasss I FranhPassal, Detroit, Micln, assignorto United Chromium, Incorporated, New York, N. Y., a

corporation of Delaware I Application November 2, 1948,

.No Drawing. 1

. Serial No. 58,026

This invention relates to cyanide bathsior electroplating copper, and toprocesses Dielectrodepositing smooth and bright copper thereirom, andprovides, improvements therein, Ad vanta ges of the bath and processaccordingwto the present invention are; H y

1. Wide limits of the free cyanide without detriment to smooth andbright deposits, and to cathode current efficiency;

Z I-Iigh current efficiency. I smooth deposits obtainable at 90 to. 100%cathode current efficiency; l p 3. Pitting'of the electrodeposit isavoided;

4,"Free rinsing properties of the electrodeposit'sf'in'aking'unnecessary aspecial cleaning cycle after' copper plating and priortobright nickel plating? I. I 1 5. Low "concentration and stability of thebrighteners used, making the .bath economical to operatej an and I 1 v7. softness and easy flow of the copper electro! deposite n buffing. 1

An example of a bath composition, together with ranges for theconstituents is given below.

Bath composition v pH approximately 12.5 to 13.5.

' odium salts are -equivalents of the potassium salts. The novelconstituent is the substance rhodanine, or substituted rhodanines, orcondensation products of rhodanine, or of a substituted rhodanine, withcompounds containing an active carbonyl (CO) group such as aromatic oraliphatic aldehyde or aldehydic acids. The particular brighteneradditive that is chosen should have a solubility in the bath of at least0.005 gram perlite'rl V v I 4 Claims. (01. 204-52) Anti-pit agents arenot required .in the bath when rhodanine, substituted rhodanine, or'acon- 7 densation product of rhodanine, is present.

Rhodanine (2-mercaptothiaaolidone-4) has the following structuralformula 'i'mui right and .1

. so 6. Wide latitude iin theopera ting temperature the interactionofaliphatic or aromatic .isothiocyanates witlithiog'lycollic 'acid'according to the following general reactiornalso' produces a powerfulbrightening effect."

ph'atic group; or' anaromatic or substituted aro- I .l': 1;';. 1;;f F f"p Examplesof specific substituted rhodanines are the fOIlOWil'ig: 1 3.x 1

eral 1 reactionwherebysuch condensation. products are formed-isthefollowing: R"f' C'O Li a 7 'R-N- oo ags zip R1 stands 101'; H; analiphatic. .or substitutedaliphatic-group, or anzaromaticior substitutedaromaticgroupl R, stands for. an aliphatic orsube stituted aliphaticgroup, an. aromatic orasubstituted aromatic :group, a. carboxyl group(.COOI-I) acetald-rhodanine 2. Rhodanine with O--hgz droa'y-m-methozeybent;-;

OH OCH: O-hydroxy-m-methoxy-benzalrhodanine RhQdaui-newi h l zlo alicemew S=L Z'=G'H (G'OH glyoxylal-rhodanine In the foregoing example of abath composiips a substitut d hedan ne. 9r. arh dan ne or ubst u d ani em den e ion p oduct; can be used in place of rhodanine, and the amountofthe subs ituted rh anineer t "1 9.. inc or substituted rhodaninecondensation;; product, when usedin plac of rhodanine, is substantiallythe same amount and range given in the aforesaid example. 50

Process conditions Range 8-25 21. p. s. f. 5 to 35. 170 F 140 to 180 F.15 ft./min. 5 to 20.

sh t r/ a l we ente l-tr mpeter 99%, 1.. Nate: e'Ihe bath will givebright depositsat currentfdensities the :low-Lpart oflthe range without,agitation, The higher current densities requireragitationh o l i It'isdesirable to continuously :filter the bath.

If ordinary precautions are taken in the operation of the bath, it hasbeen found that there is no tendency toward the formation of gas pits,striations, etc. on the cathode deposits. vHowever, if oils, greases,bufiing compounds etc. are introduced into the bath'inappreciable'quantities,- some pitting may occur in the cathodedeposits;In .such cases, it has been found advantageous toadd to the bath smallquantities of compatiblewetting or anti-pitting agents.- Ex- 75 amplesof wetting agents which were found to have been effective areproprietary substances known as Cerfak Liquid (a sodium salt of asulfated fatty acid amide) and Tergitol 08" (a sodium salt of sulfaterZ-ethylhexanol).

- Brighteners have heretofore been used in cy- "an'ide copper baths, andsome of these brighteners (thio-cyanates, for example) have been foundto be of such a nature as to cause pitting, l

though the bath may not be contaminated with striation, etc. in'thccopper cathode deposits even foreign matters such as oils, greases, etc.In the case of such brighteners, it is necessary to use wetting agentsto counteract pitting, striations,

etc. Brighteners according to the present invention do not .ofthemselves cause copper electrodeposits to be pitted or striated,wetting agents in the present bath being added only to counteract theefifect of impurities and contaminants introduced into the bath throughcareless and faulty operation practice.

What is claimed is:

1. An aqueous cyanide type of bath for electroplating copper having asits essential constituents Cu to 55 grams per liter, free KCN 5 to 13g./l KOH 7.5 to gJ/l. and 0.005 to 1 g;/-l.' rhodanine as a'brighteneraddition.

- 2. The method of electroplating smooth and bright copper consisting inimmersing agcathode aritcle in an aqueous cyanide type of bathconsisting essentially of Cu 20 to grams per liter, free KCN 5 to 13g./l., KO-H 7.5 to 30 g./l.. 0.005 to 1 g./l. rhodanine as a brighteneraddition and passing current to the cathode article at a current densitybetween 5 amperes per square foot "and 35'amperes per square foot, withthe bath at a temperature between F. and F.

3 An aqueous cyanide type ofbath for electroplating copper having as itsessential constituents Cu-20 to 55 grams per liter, free KGN-5 to 13grams per liter, Kohl-7.5 to 30 grams per liter, and 0,005 to 1 gram perliter of a brightener addition having the general for.- mula S=C2 5C=Rrin which R is a substituent selected from the class consisting ofhydrogen, aliphatic, and aromaticisubstituents, and in which R1 is asubstituent selected from the class consisting ofil) hydrogen sufficientto saturate the number five carbon atom to which said R1 is attached,(2) an aliphatic substituent connected to said number five carbon atomthrough a double bond, and (3) an aromatic substituent connected to saidnumber five carbon atom through a double bond.

4. method of electroplating smooth and bright copper consisting ofimmersing a cathode article in an aqueous cyanide type of bathconsisting essentially of Cu-20 to 55 grams per liter, freeKCN-S to 13grams per liter, KOH7. 5 to 30 grams per liter, and 0.005 to 1 gram perliter of a brightener addition having the general formula in which R isa substituent-selected from the class consisting of hydrogen, aliphatic,and aromatic substituents, and in W'hiCh'Rl is asub- 5 6 stituentselected from the class consisting of (1) REFERENCES CITED hydrogensufficient to saturate the number five carbon atom to which said R1 isattached, (2) e f01 1owing reference are f record in an aliphaticsubstituent connected to said numfile of thls Pertent? ber five carbonatom through a double bond, and UNITED STATES PATENTS (3) an aromaticsubstituent connected to said Number Name Date number five carbon atomthrough a double bond, 2347448 Wemlund p 1944 and passing current to thecathode article at a current density between 5 amperes per square footand amperes per square foot, with the 10 FOREIGN PATENTS bath at atemperature between F. and F. Number Country Date FRANK PASSAL. 49,603Denmark Nov. 21, 1934

3. AN AQUEOUS CYANIDE TYPE OF BATH FOR ELECTROPLATING COPPER HAVING ASITS ESSENTIAL CONSTITUENTS CU-20 TO 55 GRAMS PER LITER, FREE KCN-5 TO 13GRAMS PER LITER, KOH-7.5 TO 30 GRAMS PER LITER, AND 0.005 TO 1 GRAM PERLITER OF A BRIGHTENER ADDITION HAVING THE GENERAL FORMULA